text:
How is the centre of lift and centre of gravity misalignment problem solved in Delta wing aircraft?
Since Delta winged aircraft don't have horizontal stabilizers to produce down force, how is that problem solved ?

An aircraft does not need a down force on the tail for stability.
All that is required is less lift per area.

All aircraft, to maintain flight in any static, stable condition,  must be in rotational equilibrium abut their center of gravity. i.e, the sum of all pitch moments about the CG must sum to zero. Any condition where the sum of pitch moments is not zero will cause a pitch or Angle of Attack change, which will continue, either (if stable) until the aircraft reaches pitch moment equilibrium, or (if unstable) indefinitely. Lift per unit area has absolutely nothing to do with this.

The most numerous jet ever produced, the MiG-21, was a tailed delta. You appear to be asking about tailless aircraft, which is different thing altogether. Are you even thinking there is a difference between swept and delta wings in this respect? Please edit your question to clarify which you mean.

@CharlesBretana While what you say is absolutely correct, the last sentence is wrong. In order to have that desired pitch moment change over angle of attack, the relative lift per area between forward and rear surfaces / parts of the wing is what counts.

@Peter, Perhaps, this discussion, being detailed, should be elsewhere, but are you calling it wrong because of my use of the word "Absolutely"? Clearly, Only including relative values of "Lift/area" is not sufficient (how far from the CG are these lift forces applied?!), but potentially  misleading, as it is the the moments that are created, and how those moments change as AOA changes, that determines stability or lack thereof. Would you not agree?

To answer the OPs question requires that you analyze the lift *distribution" over the surface of the wing from leading to trailing edge. We use vectoral summations of the the actual, real, lift forces so often, that we forget that they are engineering conveniences used to create clarity or make calculations easier. The actual forces are from molecules hitting the surface of the entire airframe. On a  tailless delta wing aircraft, the lift forces on the front of the wing pitch the nose down, and the back of the wing creates down lift (and a nose up moment) that compensates for this.

The effect of a horizontal tail can be built into a tailless aeroplane in two ways:

By integrating into the wing profile: a horizontal s-shape with the trailing edge turned up.
By combining positive sweep with negative twist.

Because, although we often conceptualize Lift as all acting through the "center of Pressure" of the wing surface, this is a fiction, done only to aid in visualizing the total lift, and it's effects, and to aid in doing simple calculations that rely on this approximation.
In actuality, Lift itself is an artificial abstraction, as it is just a portion of the aerodynamic force acting on every square inch of the aircraft body. And this force, at each point on the aircraft surface,  creates two physical effects.

The force accelerates the aircraft, in the direction of the force is applied, according to the formula F=ma. The total aircraft acceleration is the vector sum of all the individual accelerations at each point on the surface.
Secondly, at each point of the surface of the aircraft the force applied creates a rotational force (a torque) about the aircraft CG. dependent on the magnitude if the force and the distance between the line of the force and the CG (the moment Arm)

With a delta wing aircraft the wing is designed so that the trailing end of the wing will be generating a small downwards force even when the bulk of the wing forward of the trailing edge is still generating an upwards force. Although the sum of the all the forces is still upwards, and creates positive lift, the small downwards force from the trailing edge is much further from the CG, so it has a longer moment arm, and therefore creates sufficient nose up torque to balance the nose down pitching moment from the rest of the force on the wing, which is closer to the CG with a shorter moment arm.

In order to achieve dynamic stability with any aircraft where pitch control is implemented manually through direct pilot inputs, the overall pitching moment from increasing positive lift must be nose down, (i.e., - the sum of all Aerodynamic forces must be behind the CG). This is so that minor deviations from equilibrium will create a correcting pitch moment which will bring the aircraft back into pitch equilibrium. This requires that the control surface, in order to balance this nose pitch moment, must create a nose up pitch moment. Aircraft with their pitch control surface at the tail, therefore, incur a drag penalty (tail lift down reduces  total positive (up) lift, so to achieve level flight the sum of all positive lift must be greater, increasing drag).
In modern aircraft, the introduction of computer driven flight control systems has mitigated the need for this. In the F-16 (subsonic) for example, the Center of pressure is actually slightly ahead of the CG, and creates a nose up pitching moment.  The tail surface, therefore, which is substantially behind the CG, must create a nose down pitching moment to achieve equilibrium. This means the tail is actually creating up lift as well as the wings, augmenting rather than decreasing, trim drag. Stability is artificially created by the flight control software. In flight, you can see the stabilator constantly moving up and down as it responds to small deviations in pitch, keeping the aircraft stable.

"In modern aircraft, the introduction of computer driven flight control systems has mitigated the need for this". Very few modern aircraft are aerodynamically unstable like the F-16 is. Very useful in a very manoevrable fighter jet, not so in an airliner that needs to bring people home safely.

@Koyovis, I confess I do not know which aircraft, (other than the F16), take advantage of this capability.  In addition to the increase in maneuverability, It also provides a significant reduction in trim drag and fuel efficiency. But it seems that once you have made the commitment to let a computer be responsible for flight control, with triply redundant systems, it would be foolish to not also take advantage of the drag reduction and increased fuel efficiency that this approach provides.  Do you know which aircraft (if any) use this approach?

You start right with “overall pitching moment from increasing positive lift must be nose down”, but then the part about tail creating pitch up moment does not follow—well, it does around suitably chosen point, but it can create positive lift as long as it creates less of it per unit area than the wing—nor does the part about drag—when the tail flies in the downwash, creating downward lift may still create thrust that, offsetting some of the induced drag increase on the main wing.

Most of Delta-Wing aircraft are equipped with a canard in different ways: fixed (Mirage III), movable (Typhoon) or retractable (Tupolev Tu-144). This canard is lifting surface similar to tail, which is ahead of wing and creates lift, which will produces pitch-up moment. It should be mentioned that tail's negative lift also produces pitch-up moment, which is required for trimming the aircraft.

The original Mirage iii was a tailless delta without a canard. The dual cockpit trainer version did have one.

What do you mean by the "tail's negative lift" ? do you mean the negative lift from the aerodynamic forces on the aft portion of the main (delta) wing? If so, then you are correct, and the presence of a forward canard on many delta wing aircraft reduces the need for this negative lift on the aft portion of the delta and reduces the trim drag and range/endurance performance hit from that trim drag.

There were many tailless deltas without canards, including Concorde. And fixed or retractable canards don't help with control anyway, so they are irrelevant for the discussion.


text:
Are there ways to avoid using leaded fuel in older aircraft?
What options are there for those with older planes that require leaded fuel?  Is there a relatively easy fix so that leaded fuel isn't necessary?

Can you give an example of an aircraft that requires leaded fuel?

My understanding was that aircraft engines manufactured before 1980 would require hardened valve seats and newer valve guides.  I hope that isn't true, because of the bad effects lead has on the engine, not to mention the lead, which I'm pretty sure isn't a good thing to be breathing!

In car engines it was the cast iron heads that were damaged by unleaded fuel valve recession. I expect any high alloy seat material would resist the wear.

The problem concerns older exhaust valve seats being softer than hardened seats currently used.  Lead provided a protective coating preventing the hot valve flange from welding to the seat.  Unleaded fuel removes this protection resulting in valve-to-seat welding. Upon opening the valve causes damage by plucking the weld from the seat and not subsequently closing tightly. On subsequent ignition and exhaust, the valve and seat will burn from hot exhaust blow-by.  Hardened valve seats prevent this.  But originally, it was a lead additive.  Details are in links given in my answer, below.

They don't require leaded fuel to run. The real problem is, 100LL has too much lead, for those engines intended to run on 80 octane fuel, to handle. Today, 80 octane engines are much happier running on alcohol free automotive premium unleaded.
Leaded fuel provides a minor benefit by lubricating valve seats (there is always some sliding contact as the valve centers in the seat while closing, depending on how loose the valve guides are), but aircraft cylinders went to harder valve seats some years ago the way cars did in the 80s, and seat wear is a negligible issue.
Otherwise, the lead in the fuel is nothing but grief for the engine itself and if it wasn't necessary for the octane rating, the engine would be happier without it.
Anyone with an old 80 octane engine should he using mogas if the higher vapour pressure isn't a problem (lower boiling point, and higher tendency to vapour lock).
If your concern is the introduction a new unleaded avgas to replace 100LL, it'll be happy days for all those 80 octane engines.  It's nothing but a plus to have a fuel with avgas's stability and low vapour pressure, but without the tetraethyl lead regardless of the octane rating.

You can run all kinds of engines you'd think wouldn't like mogas, even supercharged engines like the R985, and certainly non-turbo engines rated for 100LL octane also run fine on 94 octane mogas. My old glider club had thousands of hours of running "high compression" O-360s, a 100LL engine, on premium mogas.  I run my homebuilt's O-290 on mogas and it did away with having to dig the lead out of my lower spark plugs at 20 hrs after they started to misfire.  Current mogas can be a problem if the fuel system under the cowl has too much heat exposure.  I put a heat shield on my engine fuel pump.

Well, yes, there are workarounds regarding the use of leaded aviation fuel.  This link provides some answers about the use of unleaded aviation fuel in aircraft piston engines.  See this answer for a general perspective on the use of unleaded aviation fuel. The following from that answer should be noted -

In July of 2021 the FAA approved Supplemental Type Certificates (STCs) authorizing use of G100UL high-octane unleaded avgas in aircraft piston engines, without modification. At least this is something to consider, in the foreseeable future piston-engine aircraft are not likely to be rendered unserviceable due to the unavailability of leaded avgas, or the need to modify engines to use unleaded G100UL fuel.

To first answer the question. For many, almost all older aircraft you may avoid leaded fuel in one of two different ways:

Fly on mogas. As mogas is simply a mix of various stuff you take your chances that one day the mogas will be "off" enough to create a problem. (First check that all rubber components and inside tank coatings and stuff like that can handle alcohol).
Fly on one of the unleaded Avgas formulations allowed by you engine manufacturer. Type and availability varies between locations. As aviation engines has a limited life span, often on the order of 2000 hours, you could probably convert you plane at next engine change without any extreme extra costs.

Now a few words why it has not happened. There are two different problems around the move to unleaded aircraft fuel.
The first problem is related to the supply side with 100LL beeing a niche product, used in diminishing volume over time. There really is very little economic reason for the fuel providers to introduce and sell and support one more type of aircraft fuel at airfields. It is possible to find unleaded aircraft fuel in some markets and they tend to work very well without any specific problems for the airplanes that can use them.
It might be tempting to assume that you could switch to mogas straight away. And it will often work, but without guarantees. Gasoline is a mix of various stuff, where the producing plants selects the lowest price components at any time. As such there is no guarantess that mogas will have the same composition from time to time, except that it will work in most auto engines. The production might involve changing the composition so that it is "thicker" in summer (as the thicker components might be cheaper) which generally is no problem for autos. But aeroplanes fly high up where it is cold even in summer, and the thicker components may freeze. Avgas 100LL (and other aviation fuels) have specific limits on what temperature they should be able to sustain as well as how high up at lower air pressure they should not boil off. The limits for mogas are often not really defined. In addition mogas often contains alcohols, metanol or ethanol, which is no problem for a modern car but can dissolve certain rubber or plastic components used in older aeroplanes -- remember they were never expected to handle alcohols. Regardless, lots of smaller enginges and smaller operators run on mogas without experiencing problems.
The second problem is the structure of consuming side of Avgas. The main part is used by the larger two motor planes used by aviation companies for short hops or special flights. These tend to run under commercial FAA rules, meaning that they have to follow all regulations to the letter. And one of the regulations state that the fuel used should follow the engine manufacturers minimum requirements. And they seldom allow the use of anything else than 100LL for their larger turbocharged engines used in these planes that use most of the 100LL. As the engine manufacturers will be responsible, possible sued for damages, they have a difficult time allowing mogas. They could start programs to certify unleaded aviation fuel but it may need degrading performance on the large turbocharged engines -- after all the 100LL was "invented" to allow high performance. For smaller aircraft engines this has often already been done and they allow unleaded fuel. But as the larger engines have not been certified, even if the fuel company would offer unleaded fuel at airports, the largest buyers would not be allowed to use it, which sort of completes the cycle.
I believe that the change has happened already or is very imminent when it comes to smaller, private type of flying -- they can and often do fly on unleaded fuel. For the larger planes flying commercially and beeing the large buyers of 100LL my guess is that they will over time probably convert to Jet fuel instead, most probably by completing the change over to turboprops or perhaps diesel type engines.

You use premium unleaded in part for the octane safety margin, and in part because it is normally alcohol free.  You still test each batch anyway just to be sure using the simple water volume test.  In Canada at least there is no distinction between commercial and private use for an airplane with the mogas STC.  Many bush operators switched to mogas back in the 90s when 80 octane production in Canada stopped.  The air service I worked for way back started using it in their DH Beaver with no problems.

I'm not 100% sure if this is applicable to aero engines, but there are fuel additives that you can buy for older engines that provide the same anti-knock properties as leaded fuel without actually using lead (which we all know isn't great for human or environmental health!). We use such an additive for our vintage cars, about half a cap-full per full tank, and it has definitely helped the engine out, particularly with all of the different additives present in modern fuel to help with emissions, etc.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why would a pilot need to change their heading when flying through a cold front?
When doing my PPL written review there is a question, simply can't get my head wrapped around the reason why and have searched everywhere. It's definitely a very simple thing, however, I am missing the glue that helps me understand it. Hope someone can help! Thx

When flying through a cold front,_________ in order to maintain track.

This is the correct answer stated:

b) A heading correction to the right is required.

Simply can't get my head around why you would alter heading to the right going either way?

In the Northern Hemisphere, wind usually veers to the right when a cold front passes. If you fly through a cold front, the wind also veers to the right. To maintain a constant track, a correction to the right would be required.
This wind change to the right is the same flying either way through a cold front.
In the Southern Hemisphere the opposite is true. Winds generally back to the left with a cold front passage.

@OHP As far as the wording of the exam question itself, it's not like you will be out flying one day and have to think to yourself, "Ok... passing frontal boundary... change heading....NOW!"  or anything like that.  It's just to show that you can mentally conceptualize the wind pattern on each side of the front and correctly state how drift due to wind would be effected based on that understanding.

Would the caption for that chart be more accurate/general in applicability if, instead of "...surface winds blow from the south," it said something like "...surface winds blow from the equator to the nearest pole"?

@AndrewMorton I'm no expert on weather or aviation, but since a typical front (and related winds) covers only a tiny fraction of the distance from equator to pole, and since pilots are quite familiar with compass directions, "from the south" seems much simpler and more intuitive than "equator to pole".

"This wind change to the right is the same flying either way through a cold front." but in the image flying west to east the wind rotates to the left (first comes from behind, then from the right) and is exactly the opposite turn if I fly the other direction

@Federico: The (component of the) wind coming from ahead or behind doesn't affect your course. What matters is that you're either flying into wind coming from your right (if going west to east) or out of wind coming from your left (if going east to west). Either way, the wind is now blowing more from your right (or less from your left, which is the same thing) than before, and a heading correction to the right is needed to maintain your course.

"If you fly through a cold front, the wind also veers to the right." <-- I'm not a pilot, but I find this phrasing a bit misleading, because "the wind" implies "the same wind". Here's my take: "When flying through a cold front, you transition from winds blowing from your left to winds blowing from your right. So whereas you (presumably) had been compensating with a left-pointing heading correction, you now have to transition to a right-pointing correction." (Also the question not mentioning the hemisphere assumed seems sloppy, but maybe that was considered to have been to big a "hint"?)

Appreciate all the insight and all of it contributed to a better mental model and i now thoroughly understand how this works. Thank you.

In the northern hemisphere, if the wind is at your back, the low is on your left.
An air mass is a pile of air stacked up on the surface of the earth.
A front is the boundary between two air masses.
Piles of air are taller in the middle, and shorter at the edges.
Tall piles of air have high pressure in the middle. The edges of air masses have lower pressure. Therefore, fronts always occur in areas of lower pressure (troughs of low pressure). Because of Coriolis force, air circulation around a low pressure are in the northern hemisphere is counter-clockwise.
In actual practice, you fly whatever heading is necessary to maintain your course. The knowledge of the circulation of air can be helpful when planning a trip if your intended path of travel takes you parallel to a front. You would know which side of the front to be on to get a tail wind.

Appreciate all the insight and all of it contributed to a better mental model and i now thoroughly understand how this works. Thank you.

Adding to Mike's answer to address the part of the question regarding why correct to the right going both directions:
When flying from the cold side through the front, you will go from a tailwind to a crosswind from the right, and you turn right to correct it.
Going the other direction, the crosswind is coming from the left, and you have already turned to the left to correct this.  When crossing the front, you no longer need to correct to the left, so you turn to the right.

Appreciate all the insight and all of it contributed to a better mental model and i now thoroughly understand how this works. Thank you.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What can cause my radio to transmit nothing but a terrible noise?
I have replaced the noise filter and checked the jacks. It does not matter what headset or jacks are used. I replaced the audio panel and had the radio serviced. When I transmit all I hear is a low screech. Others simply reply to transmissions with a simple I cannot understand anything.
Two people can talk inside the airplane with no noise and reception is clear. I have also checked voltage and connections going to the radio as well as installed a new high quality line filter. Both push to talk switches cause the same noise, I have tried flipping things on or off running the trim etc. no change.

Being able to talk inside the airplane is not related to the radios function, the intercom (generally part of the audio panel these days) is what allows cross talk between headsets.
It sounds like you have checked all your connections which is always a good first step but after that:

Check your ammeter when the radio is in operation and make sure you have sufficient current to run the radio, if you are showing a heavy discharge on the system you may not have sufficient power to run the radio (the presence of 12V or 24V does not indicate you have enough power to run the radio)
Check your radio grounds (also lots of good info here) as they can be the source of a lot of static.
If both talk switches cause the issue (and they are wired properly) I would take a look at the radio unit its self. Perhaps have it pulled and bench tested with known good components to isolate any other factors from the aircraft. This may also assure you the radio was serviced properly when it was serviced.

Thanks, I will keep after it. When I bought it the radios worked fine. It is an LSA and I have a repairman certificate

An aircraft radio contains both a receiver and transmitter and some shared components that serve both functions. Normally, when you key TRANSMIT, the receiver is blanked (disabled) and when you release, the transmitter instead is defeated and the receiver is enabled.
The low screech when transmitting might indicate that the receive function is not being blanked, and your transmitted signal is feeding back through the receive section of the radio and making the screech.
The circuitry that does the receiver blanking is generically referred to as the PTT (Push-To-Talk) function; in inexpensive walkie-talkies the PTT is performed by a complex multigang switch which is activated by the push button on the walkie talkie. In more sophisticated radios, the PTT is activated by one switch on the mic which electronically enables or defeats a series of solid-state switches (switching logic) to do the same thing.
But in any case, this is the sort of obvious problem that a radio tech should be able to suss out quickly.


text:
Could an airliner with only one functioning engine recover from a stall?
If a modern commercial airplane such as a Boeing 787 would stall with only one functioning engine, is it possible for the pilots to right it or would it require two functioning engines?

Welcome to aviation.SE!

Does it matter whether it's on the ground?

Think about it, can a glider stall? How does a glider recover from stall?

Yes, but the challenge is managing the asymmetric thrust effects when applying power during the stall recovery.
Pilots are trained in the sim for two stall (actually, just stick shaker onset) situations: high altitude and low altitude.  Low altitude stall recovery training is normally done by slowing until the stick shaker starts, then adding max thrust while lowering the pitch attitude moderately, only enough to keep the speed just above stick shaker onset.
The objective is to minimize altitude loss while accelerating.  The training doesn't actually get the airplane to a full aerodynamic stall; pilots are trained to start the recovery as soon as the shaker goes, which is still a few degrees below the actual stall AOA (as a rule, only production or experimental test pilots will take airplanes past stick shaker right into the natural stall, or stick pusher activation if equipped with one).
I don't believe anybody actually trains for stall recovery while single engine (I never did when training on the CRJs).  In any case, if you had to deal with that, you just have the added complication of managing the yawing motions caused by the asymmetric thrust, and the much more sluggish acceleration, so in addition to managing pitch, you are pretty busy with your feet to keep the airplane straight, and you would have more altitude loss.
At high altitude, it's similar, except that the recovery maneuver is much more aggressive in the thin air. With little to no reserve power, you pretty much have to dive to gain speed, and you cover a lot more distance through space to get the same indicated airspeed rise than at low altitude, so the indicated speed increase is slower.
So you pitch over a lot more, with no effort to minimize altitude loss and you let the airplane dive and wait for the speed to come up. If you were single engine (you would be descending anyway to single engine ceiling if you were) you would be doing the same sort of fancy footwork to allow for the asymmetric thrust and keep the plane straight, to the extent that you have thrust to work with to help accelerate.
So you could say a single engine stall is perfectly recoverable, but the extra workload increases the chance of secondary problems from mishandling (like secondary stall).

Ugh; shouldn't they train for actual stall at least in high altitude because with blocked static ports, you won't get the stick shaker.

The problems you're talking about is loss of airspeed from the ice crystal blocked pitot problem.  If you blunder into an aerodynamic stall at 38000 ft, you are in a world of hurt in a lot of airplanes and in some non-FBW is unrecoverable. The training to deal with that is attitude control.  All the OEMs have QRH procedures now for flying with loss of airspeed that is based on pre-determined pitch attitude vs power values to use for different configs.  Pilots with really good airmanship skills don't really need that kind of training, but many can't cope.

A stall recovery doesn't require engines (although they help, especially if altitude is an issue). To recover from a stall, you need to lower the angle of attack. You can do this by lowering the nose until airspeed picks up, no engines required provided you have altitude to spare.

This is exactly what I was thinking. If you have enough power to thrust your way out of a stall, is it really a stall?

@AndrewBrēza Yes. It even has a name: power-on stall :). Stalling refers to the aerodynamic configuration of flow over a lift generator or control surface. Presence of thrust is an orthogonal issue. Most planes have thrust-to-weight ratio (TWR) < 1, and thus you can always lose airspeed by pitching up sufficiently, and eventually stalling when the airspeed is insufficient to keep the flow attached to the wings or control surfaces.

With enough height, any aircraft can recover from a stall without any engine power required. In fact, for under-wing engined aircraft like the 787, it is sometimes necessary to reduce the thrust, because of the pitch-up tendency this engine placement provides.
The technique in a stall recovery is always, always to reduce the angle of attack, which is easiest done by reducing the pitch attitude of the nose.

Isn't the pitch-up stall issue related to the problems of the 737-MAX?

@AndrewBrēza All stalls are "pitch up" (or, more precisely, "high angle-of-attack.") So, anything to do with a stall or preventing one will be related to pitch (or, more precisely, angle-of-attack, which is the angle between the airflow around the aircraft and the wing's chord line.) The MCAS was designed to change the force feedback to the pilots on the controls at high AoA in order to prevent them from getting too close to stall in certain maneuvers, so, yes, it is vaguely related (though it's not really related to why the MCAS didn't work properly.)

Recovery with one operative engine is possible, requiring a reduced angle of attack to break the stall, then accelerating, and adding power in proportion to the increasing rudder authority.  A slight bank toward the side with the operative engine would help, but only enough to null sideslip (center the ball) as thrust is increased.
Gradually accelerate and increase thrust.  Until the plane is able to climb up and away from terrain.  We're talking about seriously delicate flying.  Milk that mouse, bruhs.
Such a situation would result in a huge altitude loss, but that is what it would take to accelerate without much engine thrust.
Pilot flying: DO NOT YAW THE PLANE WHILE IN THE STALL
Pilot flying: BEWARE OF VMC-ROLLING THE PLANE WITH TOO MUCH THRUST FOR THE AIRSPEED


text:
Who manufactured the 737 MAX flap track fairings?
I can't seem to find the information online, would anyone of you know where / by who the flap track fairing for the B737 MAX is produced?

The fairing assemblies are made by Boeing itself. From ATS:


text:
Is it possible to (electronically) disable an ejection seat?
I'm currently reading "2034: A Novel of the Next World War" and my question may have minor spoilers:
One part of the plot comes into motion, when a F35E (the E is probably fictional) is hacked and maneuvered into a hostile airspace. The pilot wants to escape the inoperable F35 by activating the ejection seat, however, the hacker also made the ejection seat inoperable.
Now I'm wondering if this would be possible. Can ejection seats be deactivated? And if yes, why? I wasn't able to find something about this, which may indicate, that this is a bad idea to begin with. I found this answer and I would conclude, that there are indeed systems which can manipulate the behavior of an ejection seat, but nothing about completely disabling it.

An interesting "related" question: Are there any 'smart' ejection seats?.  The answer is yes, at least 1, and they had very particular reasons for deciding that it was better to act in an automated manner for that particular aircraft.

That scenario is even less feasible than the jet being taken over by a hacker in the first place. If the jet could be taken over remotely, it'd be a massive design flaw as well as just about the worst possible failure of the test program ever seen.

"So Long Mom (I'm Off To Drop The Bomb, So Don't Wait Up For Me)" - (subtitled "A Song For WW III") - a tune by Tom Lehrer, written as a hit song for WW III. Since WW III would/will/did(?) result in the end of civilization as we know/knew it, it was/is important to write such a song prior to the commencement of the war when it can/did/might still get some airplay - in the "radio" sense rather than the "radioactive" sense...

In the realm of fiction: In the 2015 novel "Ghost Fleet" F-35s are hacked in a different manner. Some of the onboard electronic components (according to the novel) were produced overseas and at least one secret backdoor was installed. The backdoor was enabled by a coded radio broadcast and turned on a secret transmitter that aided hostile missiles in finding the planes, defeating their stealth and evasive abilities. Given the existence of one backdoor, similar backdoors could plausibly exist in other systems in the plane, such as the ejection seat.

I am not familiar with the current F-35 ejection seat, much less what design changes, (real or fictional...) might be made by the year 2034, but of the three ejection seat aircraft I flew in the 1990s, none were electronically actuated such that it might be possible to hack into and disable the seat.
While they are mechanically complex, the means of actuation for most seats is actually fairly simple; relying on springs, firing pins, cartridges, and rocket motors.  It would be a very poor design decision in my mind to manufacture a last ditch fail-safe system like an ejection seat that is vulnerable to EMP, or is connected to a hackable network.

Ejection seats are the Last Resort rescue devices, actuation must be reliable.

But aren't there some dependencies? The canopy must come off first before the rest of sequence is allowed to proceed(?). What about safety features to prevent accidental activation?

@PeterMortensen mechanical linkages all the way, basically a steel wire that triggers the canopy ejection and (through spring loading to get a delay) the seat ejection a fraction later.

Or, some seats just blast right through the canopy.

@PeterMortensen probably done the old school way: Avoid adding features that facilitate accidental activation.

@PeterMortensen Safety features are only useful if they work.  In this accident a member of the RAD Red Arrows display team ejected while carrying out pre-flight checks and was killed:  https://en.wikipedia.org/wiki/Death_of_Sean_Cunningham. Apparently the seat harness straps were capable of dislodging the mechanical safety pin from its correct "safe" position in such a way that multiple routine visual inspections by different people did not discover the fault.

I wouldn't be surprised if somebody creates a seat that is connected to a hackable network and vulnerable to EMP, just for the sake of having it be electronic. At least thats the trend in every other aspect of society.

@johndoe Military applications probably aren't in as much need of that. "Control your ejection seat from this handy mobile app!" isn't a super good business model :p

@johndoe: the F-35 seat is from Martin-Bakers. They would resist that idea rather firmly.

@JohnDallman Considering what happened with putting a gigantic touchscreen in the F-35...if any military aircraft had something so daft, the F-35 would probably be a good guess.

I am quite familiar with the US-16E seat (as found on F-35) and quite a few others from the past such as the Mk 7A (found in the UK variant of the F-4).
As with all ejection seats, it is primarily an electro-mechanical system that is completely independent of the aircraft in the control sense. Obviously it is physically attached (or at least the mountings are).
In the more general sense, as with all modern ejection seats, it is a seat attached to a very powerful gun with a rocket pack underneath the seat pan.
This particular seat has an electronic sequencer that is used to determine the optimum crew / seat separation timing, the most critical of which is a 0 0 ejection. This is where the aircraft has zero altitude and 0 speed.
The sequencer is a completely closed system electronically so no remote attacks are possible and employs redundancy in the measurement and decision logic to reduce the potential for failure to extremely low levels.
The power for the electronics is provided by thermal batteries that are ignited when the seat starts to move.
The entire sequence of ejection is actually quite interesting.
Pull handle (there is only one nowadays). This fires the primary cartridge in the seat gun and also ignites the shaped charge in the canopy which blows out a large egress area.
Seat starts to move and power is applied to the sequencer which has a 'sensing window' to determine altitude and speed. Optimal separation time is computed. As soon as the seat starts to move, the drogue gun is fired. This fires a large metal bullet upwards which is attached to a drogue - a small parachute designed to stabilise the seat during descent.
The drogue won't deploy until the cord attached reaches it's limit which will not happen until the seat is well clear of the aircraft.
There are large spikes on each side of the seat above the crewmember's head which will clear any remnants of the canopy that may not have been destroyed by the shaped charge as the seat rises up through the hole in the canopy.
When the bottom of the seat reaches the cockpit sill, the under seat rocket pack fires.
At separation, the seat will cut the seat straps and tip the crew member out by firing EEDs (electro-explosive devices) to release the drogue, pulling the ripcord of the crew member parachute as that happens.
The parachute release mechanism also has a water automatic release system that will automatically release the parachute from the crew member within two seconds of landing in the sea. This is so if the crew member is unconscious, the parachute will not drown the person as it sinks.
There are some other details, but that is the fundamentals of operation.

The ejection seat and sequencing is NOT routed through the various computers. It has to work even in the event of complete aircraft shutdown, or even in the middle of the whole jet coming apart.
So no, it is not hackable remotely.

authors: Bob Jarvis - Слава Україні


text:
Why do the elliptical and the rectangular wing show different aerodynamic efficiency?
I understand the elliptical planform is aerodynamically the most efficient type of wing planform and generates the greatest L/Dmax, but it's difficult for me to understand why.
What makes the elliptical shape of a wing aerodynamically more efficient, say, compared to the rectangular type of a wing?

Does this answer your question? if not, could you mention what exactly is not clear from those explanations? https://aviation.stackexchange.com/q/39566/1467

@Federico Thank you for the link. I've read all the answers from it, but I think I'll need more time to study them before I ask you any questions. Thank you!

For a treatment of all wing attributes vs efficiency see the selected answer in https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension

It turns out, elliptical lift distribution is not the most efficient planform. It is, however, the most efficient planform in terms of L/D for any given span length, and the reason has to do with its constant span induced downwash (see For the elliptical wing, what is elliptical, and why is drag regularly distributed?).
If you relax the span length requirement and instead optimize with regards to root bending moments, the Bell-Shaped Lift Distribution is actually superior to elliptical (see derivation and NASA paper). For the same root bending moment and the same lift, the bell-shaped distribution has less induced drag.

(This may be an anti-answer.)  Why is difficult.  It's just how air flows past one obstacle or another: something that a wind tunnel can put numbers on, but not give an eloquent explanation for.  Amuse yourself with debates about the Coanda effect, which devolve into anthropomorphism.
For a given definition of efficiency, one combination of planform and washout and sweep and taper and camber and vortex generators and aerodynamic elasticity and who knows what else will outperform another.
For the famous Spitfire case, everything else being equal, an elliptical planform yields, per unit wingspan, more lift and less induced drag, over a wide range of angle of attack, than any other planform, rectangular (cheap to manufacture) or otherwise.
Theorists writing "consider a spherical cow" papers attribute this to the downwash being constant spanwise, so each spanwise sliver of the wing is working as hard as it could be.  (See what I mean about anthropomorphism.)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is the difference between a trim tab and a servo tab?
They both seem very similar but can someone please explain their main differences and principle of operation?

Related, possible duplicate: How do elevator servo and anti-servo (geared) tabs differ?. Koyovis' answer should explain it.

A trim tab is operated by an independent control to a variable position that is normally fixed once set, unless readjusted, and is done to cause the control surface to aerodynamically want to hold a position that is different from its normal "trail" position, without any input from the cockpit end.  Think the typical elevator, aileron, or rudder trim used to correct a roll or yaw tendency, or to set the "hands off" trim speed in the case of elevator trim.
A servo tab is integrated into the flight control's operating components in such a way as to drive, or help to drive, the control surface during normal control inputs.  Sort of "poor man's power steering".
You can use a servo tab to operate the control surface, that is otherwise free to trail in the airstream, completely on its own.  The stick in the cockpit is connected only to the servo tab itself.  Such control surfaces will often hang down at the bottom of their travel until airspeed "blows" the surface into its normal trail position, from where the servo tab then drives the surface up or down based on cockpit control inputs.  DC-9s and Bristol Britannias use pure servo tab operated flight controls.
Or you can use the servo tab in conjunction with a normal control circuit to boost a normally mechanically operated surface, by mechanically gearing it to move in a way that applies a local aerodynamic load that helps with the pilot control input, like having someone push on the trailing edge to help you while you move the controls.
There is a kind of hybrid arrangement you will see sometimes, called a "Spring Tab".  This is a servo tab who's input linkage is also connected to the control surface by a torsion spring torque tube, typically on an elevator system.  When you move the control in the cockpit, the control circuit input drives the surface directly, but though the springy torque tube so the surface lags the input to the extent that the torque tube twists under load.  When the torque tube twists, at the same time the input side is connected to a servo tab that displaces to help the surface move.  The surface works like a pure servo tab driven one with small inputs, but as the inputs get larger there is more of a direct force acting on the surface from the torque tube like a regular control.
This is used to get the light control forces you get with a pure servo-only driven control surface, but with the ability to still drive the surface directly to full travel when called for.  Spring tabs are popular on DeHavilland Canada transports like the Dash 7 and Dash 8.
Then there is the "anti-servo" tab. The anti-servo tab, by gearing to move in the opposite direction to a servo tab, is used to deliberately increase the normal restoring forces working on the surface when displaced from its trail position. You might add an anti-servo tab because the control forces are too light, or you want light forces near neutral but want the forces to build faster than they would without the anti-servo tab.
Mechanically operated "all flying", or Stabilator tails, such as used on the Cessna Cardinal and Piper Cherokee line, depend on an anti-servo tab to provide all of the restorative forces for the control surface, for basic stick-free static pitch stability.  They actually do double duty, and at the same time have an adjustable fixed "neutral" position, varied by the trim wheel in the cockpit, that provides for normal elevator trim (speed seeking).

Ahh - spring tabs! A moving mass + a spring = lots of fun with unintended dynamics. Great answer, covering much more than was asked for.

Thanks.   DeHavilland Canada's designers were in love with spring tabs and used them on all the bigger designs, Caribou, Buff, Dash 7, earlier Dash 8s.  The objective benefit they were after related to the STOL mission, and was low control effort at high speed where the spring tab was doing most of the work, along with good authority at low speed where the spring tab's influence waned and the physical force applied to the torque tube did the job.  A chum who flew -7s told me the main down side was the very spongy feel at approach speeds.

Don't get me wrong – spring tabs are great. But you have to know what you are doing if you design one. The fact that DHC used them so extensively testifies to the high competence of its engineers.

From this answer:

The servo tab is an aerodynamic lever. It is connected directly to the pilot flying controls.
The trim tab has a constant angle relative to the control surface. The angle can be changed by extending/retracting a mechanical link, via a trim wheel or an electric motor with a screw jack.

Seen from outside, the tabs look pretty similar. The difference is in how they are moved, the servo tab connects directly to the flight controls so that when the pilot moves the flight controls on the ground, only the servo tab moves, not the control surface. With the trim tab, the control surface moves on ground and the trim tab stays at the angle set by the trim tab actuator.


text:
Which situations would cause a company to ground or recall a aircraft series?
Which agencies or companies might decide to ground an aircraft series, and in which situations can this occurr?

There are various levels that a grounding can occur at.

Governing Agency: A legal authority can ground an aircraft make/model/serial number range (or one containing a certain part/system) if it deems they are unsafe or there is some question about the airworthiness. The most recent example of this was the recent grounding of the 787's by the FAA after the battery issue was called into question. Governing agencies can also practically ground an aircraft/make/model by issuing a mandatory AD against it; this will practically ground all airframes until proper maintenance occurs. A federal entity may also chose to not certify an aircraft for operations within a country, and/or the manufacturer may chose to not seek certification in that country although some countries allow one off certificates to be issued. In emergency situations the local governing body may shut down and ground all aircrafts in a certain area. The most prominent example of this that I know of is when all aircraft were grounded following the 9/11 attacks; this is generally more of a ground safety issue than an airworthiness issue.
Operator: The owner/operator can ground an aircraft for safety reasons if they belive there may be an issue with the functionality or operation of the aircraft in question. A good example of this is the grounding of the Southwest 737 fleet due to weight and balance issue, this was done by the airline potentially before a governing authority intervened. Another example was ANA's grounding of its 787 fleet due to engine problems.
Pilot In Command: As the pilot in command of a flight and the one responsible for ensuring the safety of the flight you can ground an aircraft for any reason you so chose and be well within your rights. Let's say on your preflight checks something is out of place or looks wrong; in such a case, the pilot can ground the aircraft until the issue is fixed.
Maintenance Persons: Generally when attacked from this angle it's more of a prevention to return to service than a grounding, but if an issue is found during a stage check or annual the aircraft may be pulled until the issue is fixed. There is an interesting article about withholding maintenance signatures here.
Recall: Manufacturers generally provide AD's instead of a full blown recall however some cases may warrant a full blown recall of airframes. When Porsche dropped the TC for the PFM3200 engine Mooney offered a recall of sorts, the owners could either sell the aircraft outright or the engine retrofit would be subsidized.

“governing agencies can also practically ground … issuing a mandatory AD against it”—they did it that way in the 787 case. FAA and EASA issued a mandatory AD saying it must not be operated unless approved modifications to its electrical system were done—except no modifications were approved at that point and they were working on them with Boeing, so it was effectively grounding it; when the modifications were tested and deemed sufficient, the AD simply became a mandatory maintenance.

I think the most recent case of a legal authority grounding a model is the Chinese authorities grounding the 737 Max-8 (which may well be what prompted the question).

If a problem is found to be common to a design or probable manufacturing defect in a production range than the FAA will issue an airworthiness directive, which requires some action within a certain time frame, the time could be immediate or at the next regular maintenance. ADs can be one time fixes and inspections or continuing. Aircraft manufacturers can also effect the same directive for inspections or maintenance by issuing a revision to the operations and maintenance manuals.(as the FAA requires compliance with the latest manuals) The issue may be due to the base product or due to difficulty with adequate compliance in the field.
In the USA an individual aircraft is grounded anytime it is not legally "airworthy", this can be wide range of items and can be conditional on specifics of the intended flight: not having the registration card, operators manual, or other documentation; mandatory FAA inspection, maintenance, or modification directives "airworthiness directives"; not meeting the mandatory minimum equipment list; even a required inspection one hour overdue; parts found in questionable condition during the pilot in command's preflight inspection will ground the aircraft until addressed by the correct engineer/technician(who may approve the condition as not a safety hazard, make a temporary repair to be further addressed at the next inspection, or full repair on the spot).
Sometimes grounding is conditional on flight conditions, if your attitude indicator not functioning (and properly labeled as broken) the plane is not airworthy for instrument meteorological conditions but it is airworthy for visual flight conditions.
Other times it could be conditional on the purpose of the flight, a flight for hire(regulation 135 or 121 operations) will have different requirements from a general flight(part 91 operation) for private or internal company business. It could also be based on pilot currency, the plane may have operational equipment for very low visibility landings but the pilot has not practiced this combination within a certain time-frame then the plane-pilot combination cannot fly for hire under those conditions and is effectively grounded until forecast conditions improve or a pilot that is current with the equipment and conditions can be called in.
Also special ferry permits can be issued to make an aircraft airworthy for a single trip under specific conditions. Ferry permits are most often to move an otherwise non airworthy aircraft to a maintenance or inspection facility; using minimum crew, no passengers and no paying cargo, in good weather during the day on a route that avoids dense population areas. They may also be used for odd cases like a new aircraft that has yet to be registered to the owner.
In many top tier companies and nations, there are "no fault" rules to protect pilots for retribution based on any safety related decisions. That is if a pilot doesn't like the sound of the engine and refuses to takeoff until it is fixed or aborts a landing or diverts to a different airport because of landing, the pilot will not be punished in any way. However this is not the case in all countries and companies, in some places they do not have much of a safety culture and pilots will be quickly replaced by others who only consider the immediate cost to the company.(coughAsiacough) To such an extent than the EU has blacklisted several airlines for extended periods(many years), such as Lion Air. The FAA does not blacklist outright but it does assess some airlines as "not being in compliance" with international standards and recommends US citizens travel direct on more reputable airlines. https://www.businessinsider.com/lion-air-banned-from-the-european-union-2013-4 I do not want this to mean that all airlines from a region are bad, there are good airlines in all regions, but the prevalence in certain areas is notable.
I had a longer answer but cut my self short as I was kind of leaving the specific question and going into general safety trends in the airline industry.

When you are talking "aircraft series" it suggests a worldwide grounding of an entire fleet of a type.  This will be normally be implemented by the OEM's regulator in consultation with other affected regulators (generally when one issues an AD the others automatically adopt it) and the OEM.
When a safety incident or crash happens it triggers an airworthiness process between the manufacturer and the regulator of the incident country and manufacturer's home country (usually led by the home country's regulator/investigation authority in coordination with the crash host's).
There is a standardized mathematical risk process that is followed to determine what mitigations are required, and how soon they are required, and whether interim mitigations can be applied, to reduce the risk of a follow-up event to an acceptable level.  At one extreme, you have ground the fleet right now, and at the other end, you might just have a procedural change.
Grounding an aircraft series, as the most extreme action, is done only when the existing risk is so high there are no procedural mitigations or maintenance actions that can be done until a design change can be installed.  They try to avoid this at all costs, but in rare cases, like the 787 battery fiasco, there is no choice and they are forced to issue an AD with no mitigations or phase-ins that grounds the fleet until a Service Bulletin with kits is issued.


text:
How is altitude correlated with true airspeed?
I am trying to understand the BADA 3.0 dataset (specifically I am looking at Performance Summary Tables):
E.g.

What is not obvious to me is why those tables mention only single TAS for specific FL.
Is it true that for a given specific aircraft there is a single specific TAS that aircraft can travel on given FL (due to wings lift forces produced, etc)?
I thought aircraft are capable of traveling with a range of speeds at given altitude depending on Angle of Attack (AOA).
Or maybe what I am looking at is just a summary table that does not cover all possible values, however, those are the only one FL+TAS pairs that makes sense in practice (as flying otherwise would be highly inefficient).

This probably refers to flying at a fixed IAS (indicated airspeed) or Mach number, which will result in different TAS depending on pressure or temperature. Note the fixed Mach 0.80 at the top left.

How could I possibly use that dataset to estimate fuel consumption for different speeds than Mach 0.8?

Good question! The TAS scales linearly with Mach number (since Mach = TAS / speed of sound) for a fixed temperature, but the fuel consumption can change in complicated ways (depending on specific aircraft and engine parameters). Probably, there is no generic answer to this...


text:
Can anyone identify this plane?

Can anyone please help me identify this biplane? The photo was taken in Newcastle, NSW, Australia. I can’t seem to find anything.

Welcome to Av.SE!

No brainer, Tiger Moth or Gypsy Moth, this is not hard, overall shape strongly suggests the former.

It looks like A17-647/VH-BGR, based at Luskintyre. The same aircraft, though not easy to match :-) History. There is a Tiger association there, flying their Tiger once a month in the vicinity.

Looks very much like a de Havilland DH.82 Tiger Moth.
This webpage lists all Tiger Moths used by the RAAF.


text:
Are there a toilet and (small) kitchen in the Su-34?
It seems that there are a toilet and small kitchen in the Su-34. The Su-34 is a medium range fighter-bomber with a range of action of 4000km able to transport 8 tons of bombs and missile.
I know that the pilots enter from the bottom and they sit side by side (so there is some space). Some people say that there is a toilet, some other comforts (microwave,bed) and others say that there is just this:

Is that a toilet? Can you confirm if the Su-34 really has those features?

I dunno, there seems to be a urinal in my hang glider.  At least, I managed to take care of the issue in some way and my clothes didn't get wet; not sure I can say the same for the people down below on the ground.

This question needs heavy editing, because the pictures are wrong. However, the Su-34 does indeed include some minimal amenities. I'd vote close if there was a duplicate, but curiously one is missing.

@Ralph, I can understand your point, but I disagree that the question includes deliberate dis-information.  I think the photo was included as an example, and a minor edit would make it acceptable.  (otherwise, why ask the question if you truly believe you have photographic proof?)  And dispelling dis/mis information is on-topic...

I've edited out the irrelevant photo. The other photo is from the Su-34.

The photos are just that i have find.....because i did not know the right and wrong!

Yes, the Su-34 does technically include a food ration warmer, a "sanitary container", and some room that allows for sleeping.
However, all three are much less impressive than the terms might suggest:

The food ration warmer is not a microwave. It's just a small can heater:

There is also some dedicated room for extra cans.

The "sleeping room" is just a bit of room where one could fit a sleeping sack.

One can lay down their head and torso on the entry hatch and fit their legs between the seats. This may come in handy for really long missions, likely with in-air refueling. This is more of a side effect of having an entry ladder and a hatch than a deliberate amenity.

The "toilet", or "sanitary can" as it's called, is exactly as illustrated in your question. Its interface technically supports both methods, but there's no record or hint of anyone ever using any but the first.

The reason for these is that the Su-34 is meant to be a long-range bomber with enough air-to-air capability to fly unescorted. So, even though based on a modified fighter platform, it was fitted with minimal amenities. However, these amenities are more of a "tick the box" type.
P.S. To correct some premises, ~8,000 kg is the payload limit for most of the Su-27 family, but not the -34. The Su-34 is significantly above that, with a maximum payload of 10,400 kg with maximum fuel or 12,500 kg with reduced fuel. In practical usage, it's an attack aircraft/bomber that can defend itself and operate against extensive air defenses.
To have an idea of where such a concept comes from, look at the Tu-22M. While a strategic bomber by role, it's rated up to Mach 2 and 2.5 g, has basic defensive armament, and is meant to engage aircraft carriers. So the VVS idea of a bomber from the 1970s on has been less of a bomb truck and more of an enlarged fighter with a large payload of guided munitions.
The Su-34 is a further development towards a fighter-like bomber direction. It's a heavy fighter platform with added wing area, range and payload to match older bombers. To narrow down its role, consider the F/A-18 for a comparison as an exemplary fighter-bomber that you'd see deployed on A2A missions as easily as A2G. The Su-34, OTOH, is more of a fighter-based bomber that doesn't need a fighter escort, but complements the base models for A2G and leaves A2A missions to Su-30/Su-35 variants.
P.P.S. I've taken the liberty of editing out your 2nd image, as it's from a space station.

The answer is no. The SU-34 is a tactical jet with ejection seats. There is no room for such amenities.  Most fighter type aircraft only have a relief tube of the type in your upper photo.

So there us just the object of the first picture. it's a simple cylinder filled with chemicals for odors.however there is a bed behind the pilots normally

Well that’s not entirely true.  The B1 bomber was equipped with a small commode just behind the commander’s seat, despite being equipped with ejection seats at all four crewmember stations.  It’s not unreasonable to think that an Su-34 would or could be similarly equipped.

I seriously doubt there is a bed in the SU-34.  If you have proof of this then please post it.

@CarloFelicione It is indeed true. There is no room for such amenities in the SU-34.

The B1 is a lot bigger than the SU34, and obviously must have been designed with this in mind.  I don't know the history of the development of the Su34, but just looking at it I would wager it was adapted from a single seat fighter design.

No, there is neither a toilet nor a kitchen on an SU-34. The first picture in your post is of the "relief tube", which the crew can urinate into. It's not a toilet, though, and can't handle feces.
There is a small area behind the crew seats just big enough for one person to stretch their legs, which can be used to store food if the crew so desires. It even has a dedicated bracket for a single thermos. Though I would hardly call that a "kitchen", since it doesn't have a refrigerator, oven, water, cutlery, or anything else that kitchens usually have. It also doesn't have a bed.
The second picture in your post is actually from the MIR space station, and has absolutely nothing to do with the SU-34. I don't know where you even got it from.

A picture would add a lot to your answer, if you can find one.


text:
What is the cruise altitude of the Beechcraft Model 18?
I'm trying to find the cruise altitude of the Beechcraft Model 18 (S, Super H18 or any variant), or the range of altitude for such aircraft.

The maximum altitude of a Beech 18 is about 20,000 feet (at 20,500 feet), but you can expect most Beech 18s to fly at around 7,000-9,000 feet.
Source: https://www.planeandpilotmag.com/article/beech-model-18/#.XpSqwshKiM8

As I remember, Beech 18s are unpressurized. As such, I doubt you'd often find them in cruise at altitudes requiring the crew and passengers to be sucking oxygen. Are there pressurized variants of the Beech 18?

@Terry You could technically manually install pressurization, but I don't know if Beech offers it. But there are actually plenty of Beech aircraft used for skydiving, which results in them giving oxygen to the passengers. But, you are partly right, maybe not 18,000.

@Terry welcome back!

@aircanada001 pressurization would require a complete structural redesign of at least the fuselage. This would drive recertification of the aircraft, which would be impossible since it doesn't meet modern design standards. If you pushed through all that what you'd end up with would no longer be a Beech 18.

okay then @pericynthion


text:
What is this part on a Cessna 172 engine?
Can any one tell me what this tube with the red is? This is a photo of a 1977 Cessna 172 engine. Looks like the tube is directly connected to the top of the crankshaft.

Your other question asked about identifying parts for your checkride. For PPL and under, a DPE is not going to ask you about this part. If this part is not on the preflight checklist and/or FAA ACS don’t bring it up in the checkride. You are not an A&P. What is the real reason you are poking around this airplane?       https://www.faa.gov/training_testing/testing/acs/media/private_airplane_acs_change_1.pdf        https://aviation.stackexchange.com/questions/78803/can-you-identify-these-antenna-items-on-the-belly-of-a-cessna-172

He's just looking in the cowling inlet and wondering what it is.  I would certainly want my students to get to know their airplanes mechanically.

@JohnK - Knowing the aircraft mechanically is great. I volunteer at my A&P’s shop for my own knowledge. But, per his other question, he is about ready to take his checkride. His time is better spent on other things besides this minutia. And, he has a CFI who he can ask questions to fit the DPE’s gouge. After his checkride, he should ask the local A&P if his CFI can’t give him the answer. But, not right now, IMHO. And, that part is on the firewall, not the cowling inlet. He is doing a lot of digging in the wrong places.

Fair enough.  On the part, what he is asking about is the orange-y elbow which is at the just forward of #1 cyl, front left, and you can see that in the inlet as it's right near the front (that is #1 cyl because you can see the hoisting fitting on top to the rear a bit, which is between the cyls). The bulkhead at the back where the oil line passes is the engine baffling bulkhead not the firewall.

Are there really CFIs who DON'T train students on this? It's part of understanding the basic operation of a four-stroke engine.  This is basic PPL knowledge.

NOTE: Revised in response to poster comment: The engine is a Lycoming O-320 D2G, part of the series that replaced the disastrous H2AD engine which that '77 172 originally came with, in 1981 (the H2AD was '77 to '80). The H2AD engines (I have to think some joker at Lycoming put the AD designation in as a gag — it had a number of ADs against it), among other problems had a very small valve lifter contact face that would spall very quickly and trash the camshaft (on the plus side, you can remove the lifters without splitting the case).  Most 77-80 172s have had their H2AD engines replaced with Ds, which went back to the old lifter design, which also applies to the airplane pictured.
Anyway, the fitting is tapping into an oil gallery that supplies the valve lifters and has a plug at each end.  Someone has removed the plug at the front and installed the elbow to run oil pressure back to a cockpit indication, possibly because the port normally used on the accessory case is being used for something else.

One of the airplanes I fly is a 1977 C172N with the Lycoming  0-320. It has the constant speed prop STC. I always figured it was more of an odd duck than the norm. Have you run into many of these, yourself? I’ll have to check that tube next time the A&P pops the cowling. Also, do you have issues with this particular models prop control? The knob on ours is always very, very stiff. Even after warm up. It rotates easily. But, back & forth movement is sometimes an issue.

Myself I've never seen a 172 with a CS STC in person.  There will be about a 50-75 lb weight penalty when you do that due to the extra weight of the prop and governor and those STCs never include a compensating gross wt increase.  Not something I would do if I owned one, just to get a bit of extra performance.  The tube will be visible just looking in the right cowling inlet when you check for birds nests and such during a walkaround.  The prop control will be some generic vernier control.

There was no GTOW increase to account for the prop, hub and governor. We never had more than two people in it anyway. The performance increase was decent, but nothing to rave about. On the other hand, the fuel economy was outstanding if you leaned it right. Very much worth the weight penalty if you were renting it by dry-tach rate for time building. If it did not have alternator issues, and had a better panel & stack (an ADF, 1 non-WAAS 430 and a LORAN), I would still be flying it today. I moved up to a 172SP with a G1000 for my instrument training.

In Canada when you do an instrument rating, there are separate ratings for single (Group 3), multi (Group 1), and center line thrust (Group 2 - Skymaster et al). You have to do your IFR check ride in the type based on the rating you are after.  So if you want a multi-IFR, you so a multi rating, then finish the hours for the multi-IFR and since you're doing the check ride in a twin, you end up doing most of the hours in a twin.  The check ride will include an engine failure while executing a missed approach.  When I did my mult IFR some years ago I only did cpl hrs in a 172, rest in a Seminole.

@JohnK Thank you for your answer. But the plane does have a fixed pitch propeller. The engine is actually a Lycoming O-320 D2G. After digging through the installation directions I found that it is an oil pressure reference line.

@CharlieEcho Thanks for the update. That's odd because the oil pressure port for the cockpit indication is normally back on the accessory case.  That fitting then is tapped into the end of the oil gallery that supplies the valve lifters, which is plugged at each end.  The propeller gallery port/plug is right next to it just out of view.  I've never seen a cockpit indication pressure line run from that spot before.  Maybe the accessory case port was being used for something else. I've revised my post to correct the information.


text:
Does the 737 MAX's engine nacelle camber affect the pitching moment?
A side view of the B737 MAX's engine nacelle shows a positive camber at the top. As nose camber of any lifting shape (wing or nacelle) generally allows more lift at higher AoA, do you think this feature plays a role in the nacelle destabilizing pitch up moment?

I think it's more because there's this very big engine whose thrust is not on the center-of-drag of the aircraft. The thrust is lower and forward, the drag is upper and back, it adds up to a rotary motion.

The question is not on the nacelle position effect, but on the different shape of the 737 Max nacelle vs 737 NG. A nacelle is a very low aspect ratio lifting body, able to very high AoA without stalling - and nose camber may add a lot to this point.


text:
How is ATC handed for private rural airstrips?
In rural Australia there are farms that have private airstrips. My question is when an aircraft wishes to land at such a strip (for example a flying doctor) who handles the landing aspects of ATC.  Things such as reporting on wind speed and direction, air pressure, ensuring that the strip is clear, advising on glide slope?

Welcome to aviation.SE! This question might help, it isn't specific to Australia but it's fairly general. If you're new to the site, the [tour] might also be helpful.

I can’t speak for Australia, but in the United States there are thousands of uncontrolled airports throughout the country, both privately and publicly operated.  Larger, better equipped public uncontrolled airports have good facilities such as paved runways and taxiways, instrument approaches, automated weather reporting stations, pilot controlled airport lighting, FBOs, fuel and maintenance depots, etc. but many uncontrolled airports are simply grass, gravel or dirt strips with little or no facilities, particularly in back country or mountainous areas.
Typically the decision to go into these kinds of airports is at the pilot’s discretion and the pilot alone must make the final call as to whether they can safely take off and land at these locations.  Bush pilots departing from said locations will typically carry small handheld weather stations used by mountaineers for determining local atmospheric conditions, winds, etc.  Remote airports will use a standard left hand traffic pattern flown at 1000’ AGL, but many do not due to nearby terrain and are one way in/out.  If a CTAF is not published for the airport, pilots will use the MULTICOM frequency of 122.9 MHz to announce their position and intentions.
Condition of the airport and runway are often not monitored and it is up to the pilot to determine if they can be used.  Arriving traffic will often make a low, slow pass over the airfield to determine runway condition and look for obstacles which could impede landing.
All types of aircraft can and do use such airports but most often the aircraft operating from them are specially build bush aircraft with good STOL flight characteristics plus beefy landing gear and tires for operating from unpaved strips or off field operations.

I can speak for Australia and can say that these procedures are almost exactly the same here, except FBOs are virtually unheard of. You've got to do everything yourself.

There is very little air traffic control for such airstrips* precisely because there is very little traffic.  Even a popular semi-backcountry strip, say Smiley Creek in Idaho, might see a dozen or two planes on a summer weekend.  You just use your eyes, and monitor the CTAF and announce your intentions.  Other places I might land and camp for several days without seeing another plane.
As far as weather &c goes, it's pretty much seat of the pants.  You look at the wind sock if there is one, or other indicators such as sideways drift when you try to fly a straight course - say when you're making a low pass over the runway to check on condition, and scare deer, cows, antelope, or whatever.  (Probably kangaroos in Australia :-))  Then you make a judgement call as to whether you can handle it or not.
As for glide slope, if you're flying a light plane in VFR conditions, you eyeball it. Larger but still uncontrolled may have luxuries like VASI/PAPI, or even pilot-controlled runway lights for night landings, but smaller strips don't.
*At least in the US: I'm not familiar with Australia, but don't see any reason why it should be different.

As far as weather &c goes typo?

@kevin nope, just an older way of writing "etc."

@FreeMan: Not so much older, but one that frustrates simple-minded typesetting algorithms that can't tell the difference between the period of an abbreviation, and the one at the end of the sentence.

Pardon me, "more obscure". :) Your point is excellent, however, about avoiding the autocorrect autocapitalizing the word after an abbreviation - I hadn't thought of that one. I don't often text "etc", but I will use "&c" from now on (when I remember) to avoid that minor annoyance. (Or, I'll just skip the period as I did there without realizing it.)


text:
Do ferry flights to the US that are not ADS-B Out equipped require a special ferry permit from 1 Jan 2020?
The aircraft is not compliant with ADS-B Out DO 260B and will be parked in Arizona after return. Can this aircraft fly to the State for ferry flight only to US without ADS-B Out DO 260B? Should I apply to FAA about ferry special permit in advance?

This depends on what "State" is (more specifically, your route of flight)... You can also make the request to the controlling ATC to transit the airspace at least 1 hour prior to the operation if you do not have ADS-B, if it is a long flight, this may be a lot of phone calls. I don't believe a ferry permit is required (unless for other reasons).

You probably solved this by now, but if you keep the aircraft away from Class B (30 NM) and below 10,000 MSL, you don't have to have ADS-B.


text:
How do humanitarian flights arrange special permissions to fly when ATC isn't available?
In natural disasters, transportation infrastructure is often among the first and most critical of public services to be disrupted. Not coincidentally, it's also a time that tends to see small airports become vital intake for international support.
If aircraft acting on humanitarian concerns, say a commercial airliner loaded with doctors and medicine, wants to land in a major city affected by a natural disaster where radar is destroyed, ATC is non-functional, and runways are... surprisingly clear, what is the procedure for arranging landing?
In practice, do humanitarian support just approach, land, and deal with the consequences later?

I flew to Libya under humanitarian support in 2013 when there was a civil war going. We flew with the technician to operate cargo doors and one cabin crew to support us. We were carrying a cargo of medicine and food with Airbus A320.
It may not be the complete answer of yours but we followed a special procedure as;
Malta control was the closest and working ATC with full radar coverage until the shore. They had phone contact with Tripoli tower. Tripoli airport is very close to the shore line. The weather was VFR and they provided wind and visibility which is enough. Malta radar made us decent to 10,000 ft. at the exit point and hold for confirmation with the guy in the tower. After 10 min. he gave us a clearance as;
"You are cleared to VFR approach and land in 20 min. vacate runway from the end, backtrack on parallel, cargo operations waiting on parallel runway touchdown side. Take-off time xx:xx zulu, after take-off runway heading 5000 ft and right turn to XXXXX point. Contact Malta Radar."
So there will be no navaids, no ATC and no radar that follows you. But the Malta radar was following us almost all the time. Also, you still need to follow non-ATC operations, which means blind transmitting all the time.
We flew to GPS coordinates of the airport and descent to 5000 ft. when we see runway, we joined the visual pattern.

Thank you for an experienced based answer.

In the U.S. at least, HADR doesn't launch aircraft until a crisis aka disaster has been identified, even if at launch they don't yet know if the problem is lack of potable water or civil unrest over rigged elections.
An already flying commercial airliner won't have a glut of doctors and medicine unless it's been chartered for an already identified crisis, so it's unlikely to divert to this one.
If, after an identified disaster, an aircraft flies there to assist:

A helicopter doesn't need ATC support to land in an off-airport parking lot, of which a major city would have many.
A fixed-wing aircraft, needing an approach path, lacking ATC response, would revert to non-ATC protocols, just like at a small Midwestern grass strip or an Alaskan inlet.  VFR.

Non-aero analogy:  fire trucks and ambulances don't fret over parking tickets.

I agree, before you send any sort of commercial jet you will send in a load of specialists to get it ready for them, including setting up some sort of ATC.

Or even not so small grass strip—there are untowered airports with paved runways and scheduled flights of Q400s and ATR-72s.

No ordinary commercial flight will land at an airport in a disaster zone as you describe. However, it isn't impossible, and special crews trained in disaster relief operations do it all the time.
First of all, ATC is not required. All pilots are trained in landing at uncontrolled (aka pilot-controlled) fields, which comprise the vast majority of airports. The US alone has ~15,000 airports and only ~500 of them have a control tower. And most of those control towers close at night.
Secondly, ATC does not need radar, just radio sets which are easily flown in if all the ones on the ground are destroyed. The FAA even sets up temporary towers for air shows or fly-ins at normally uncontrolled fields. Likewise, the US military (and presumably others) practice landing at fields in hostile territory, securing them and setting up ATC operations. Radar improves safety, efficiency and capacity, especially in bad wether, but even most towered airports have no radar coverage.
Therefore, the actual humanitarian flights, even only a few days after the disaster hits, can have a relatively normal aviation support infrastructure available. It's the ground situation that keeps normal (scheduled commercial) flights away.
The obstacles are primarily legal and political. While many countries are quick to accept assistance, some are not. Getting permission for the flights themselves, customs waivers for the cargo and visas for the relief workers can sometimes take days or even weeks depending on political issues—and nobody is flying in until they're sure they won't be shot at, either by the local military or militia groups that may have taken advantage of the disaster. There may also be insufficient ground infrastructure to move supplies and workers from the airport to where they're actually needed as well.


text:
Do military pilots use amphetamines or other stimulants?
Related to this question: Do military pilots have flight & rest hours regulation?
According to the wikipedia article, amphetamines were commonly given to Allied pilots.
Are they still in use today?

I would guess they are, but nobody really wants to talk about it. They were certainly used a lot in WWII, to the point that German pilots showed symptoms of overdosing with Pervitin (colloquially called "Kanalkoller").

The U.S. Air Force (and Navy) still uses, and has used off and on since WWII,  what are commonly referred to as "Go Pills" for instances when pilots need to be up for long periods of time - in wartime, sometimes longer than the crew rest regulation. (These pills can also be used for altering sleep cycles, along with "no-go" pills; for example, when changing from day to night).
The most common go pill is Dexedrine, which is an amphetamine. You can find some more information in this article.

When I deployed to Korea for the first time, I did the flight surgeon test of the go and no go pills.  I really didn't notice much of an effect from either.  But yes, SSumner is 100% correct.

I've tested the no-go pills, and they had minimal to no effect on me, but one of the others in my squadron told me the tested ones are low dosage and only to test for allergic/adverse reactions. The real things are stronger.

I would like to add that these 'go-pills' are nothing more than Adderall! (Dextroamphetamine!) (In other words nothing more than the average ADHD student such as myself takes. Ironically, I take Adderall and thus am not allowed to enter the military because of it.

That is quite ironic considering that my prescribed Adderall would prevent me from passing an FAA medical and getting a PPL.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Is it true that different variants of the same model aircraft don't require pilot retraining?
I'm referring to this Wendover Productions video - The Economics That Made Boeing Build The 737 Max.
The creator asserts that designing a new long range narrow body plane would be more expensive than modifying an existing design, which is uncontroversial enough.
But he also makes the claim (timestamp 6:13)  that there was pressure from American Airlines to provide a re-engined 737 over a new model, because existing American Airline pilots are already trained to use the 737.

Pilots are generally trained to operate just one type of aircraft. Some fly the a380, some fly the 777, some fly the a320, and some fly the 737, but they don't fly the 737-700 or the 737-800 or the 737-900, they fly the 737 airplane as a whole.
Pilots are trained to the aircraft, not the specific aircraft variant.
In general, pilots can and do switch between variants of aircraft even in any given day and are not required to do any substantial training to be certified on different aircraft variants.
Crucially, the FAA has never required that 737 pilots complete any simulator training before flying new 737 variants.
That's because a 50 year-old 737 more or less flies like a 1 year-old 737.
American [Airlines] wanted a refreshed 737 over a new plane since they already had thousands of trained and certified 737 pilots.
They had no pilots for a hypothetical new narrow-body Boeing and the cost of training their pilots to a new plane would be massive.

Is this characterisation correct, or is there some nuance missing here?
The thing that I'm finding a little hard to understand, is that these different variants of aircraft must have different handling characteristics, or different things to consider (ie. things unique to doing a longer flight), it does seem a bit crazy that no training would be required.
It also seems that the economic incentives are a bit backward - this kind of dynamic would stiffle aircraft innovation as a whole.

The question is about pilot training, but the other big issue is certification. With a 50-year old basic design, there is a huge economic incentive to make design changes that can be certified using "grandfather rights" instead of having to re-certify to current regulations. When that tail is wagging the design engineering dog, you can end up where the 737 Max has ended up.

… Of course you can argue that the 50 year safety record of the 737 family is better data about safety than any new-aircraft certification program, but the rules have to be the same for everybody - though arguably the entire concept of "grandfather rights" is in practice a not-so-subtle form of national protectionism, given that the F in "FAA" standards for "Federal" and Airbus doesn't (yet) have any 50-year-old aircraft designs.

Related: How are evolution and variants of aircraft considered by certification authorities?

This question brought to you by the letters M C A and S.

It appears to depend on how much changed. You do have to have some training between models. The selling point was that an airline with 737 pilots could fly the MAX variant with minimal retraining

"The airplane is configured to be very common with the [737 NG]," Wilson, who is now retired, said, "and so a pilot can walk into here and will find everything he can just like he can in the [737 NG]."
"FAA-approved this for two-and-a-half hours of computer-based training for the transition between the two aircraft," Wilson continued. "All the overhead panel switches are the same. The only minor difference is, because of the change in the display, is to move some of the center console items here on the forward console."

And from the Wall Street Journal

To make the plane as inexpensive as possible for airlines to adopt, Boeing was intent on persuading regulators that pilots of earlier 737s should be allowed to start flying the MAX without simulator training. That training would have been required if there were substantial safety differences between the models, boosting the plane’s cost to airlines since training cuts into time flying paying passengers.
  “Our marching orders are no training impact on this airplane. Period,” Richard Reed, a former Federal Aviation Administration engineer, recalled a senior Boeing official telling him during a meeting in the early years of the MAX’s development.
The company had promised its biggest customer for the MAX, Southwest Airlines Co. , that it would pay it $1 million per plane ordered if pilots needed to do additional simulator training, according to Rick Ludtke, a Boeing engineer who worked on the jet’s cockpit systems, and another person who had been involved in the airplane’s development.

And later

Boeing officials were focused on making the MAX fly as similarly as possible to earlier 737s. The fewer differences, the less likely the FAA would require pilots to undergo retraining.
Mr. Ludtke, the former Boeing cockpit engineer, said company managers put pressure on engineers to avoid tweaks in designs that could result in pilots needing to learn new maneuvers in a simulator.

Wasn't there a difference?
The issue was that the MAX had a system (MCAS) that could push the nose down to make it behave more like previous 737s. Having read several articles on it, the root problem was

The initial specs said it was a minor change with the same course of action to correct as a runaway stabilizer (i.e. it was something 737 pilots already knew)

The company reasoned that pilots had trained for years to deal with a problem known as a runaway stabilizer that also can force the nose of the plane to dip. The correct response to an MCAS misfire was identical. Pilots didn’t need to know why it was happening.

Boeing made MCAS 4x more powerful without really notifying anyone. It could also operate at slower speeds.
Boeing apparently wrote its manuals based on the original MCAS spec. Assuming it was still a minor system, it was buried or omitted

Southwest Airlines, the jet’s first and biggest customer, followed Boeing’s lead and deleted MCAS from the manuals and emergency procedures it devised for its pilots. Other carriers didn’t mention it, either.

As predicted, the previous crew of the aircraft that would be Lion Air 610 had issues with MCAS, but correctly diagnosed a runaway stabilizer and shut off MCAS in the process

The puzzled cockpit crew checked a quick reference handbook, running through other emergency steps before successfully regaining control of the plane by executing the checklist for a runaway stabilizer. That turned off MCAS and the crew flew manually for the rest of the trip.

Lion Air 610 would not be so lucky. They only figured it out moments before the plane slammed into the ground. Apparently it wasn't as obvious to pilots as Boeing thought.

The MCAS was not, actually, the problem but rather the solution. The problem was that the MAX needed bigger engines, which had to be mounted further towards the nose of the aircraft (to still fit under the wings). This new position would cause "issues" with the stability of the aircraft - notably, the nose would rise unexpectedly. The MCAS had to be added to actively counter that issue. There was just the minor detail that some pilots "who were not initially informed about existence of the new MCAS system" were a bit...surprised.

There was also another less public info regarding the recovery plan requiring the pilots to make the correct decision in 4 seconds. When they tested the revised MCAS system (2019), the pilots made the correct assertion in 4 seconds and recovered the plane, but this is not a good margin of safety and so that's why the entire concept of requiring perfect pilot response is being revised. The Lion Air pilots turned off the MCAS and then turned it back on minutes later, dooming their flight.

@Nelson I believed they turn off motorized trim not the MCAS as such, because manual trim was just too physically expensive

Firstly, some terminology:
A class rating allows a pilot to fly a certain class of aircraft (Fixed wing, Heli, gyro-copters etc.). Whereas a type rating allows a pilot to fly a certain type of aircraft (A320, 737, etc.). I believe this is the same all over the world as it is ICAO.
I can't answer for the FAA rules as I have no real experience with those. But at least, here in Australia, CASA (our civil regulator) lumps together all 737s from the 737-300 to the 737Max into one type rating.
They do however have a requirement for differences training, which was the "iPad video the transitioning pilots had to watch" - as far as I know there is no real prescription for what this training consists of.
Another interesting side effect of this legislation is that a pilot can fly an ATR42 and ATR72 on the same type rating, despite one being almost 2x the size of the other in some configurations!
SEE https://www.legislation.gov.au/Details/F2018L00660

Other examples...757 and 767, A40-300/200 and 600, A350 / A330.

Wow, I had never seen that! Really goes to demonstrate the importance of proper regulation and type certification when introducing an airliner on the same type rating!

Where the regulator allows a common type rating but requires differences training among different models within a type, a major priority of the OEM is to limit the training to videos or CBT (computer based training). They will pull out all the stops to avoid a requirement for dedicated simulator time, as this has a significant cost impact for an airline and screws up the commonality benefit to a degree and can really hurt sales (this is specifically what Boeing was trying to avoid in the MAX).
On the CRJ regional jet program there were some interesting aspects to this.  The CRJ200 has a hard leading edge (no slats) and lands VERY differently, technique wise, than their slatted 700/900 relatives, but Bombardier was able to avoid dedicated sim time, and just requires a video (which really may not be enough; hard landings have been a problem with pilots transitioning from 200 to 700/900 - you go to idle much sooner on the 200, crossing the threshold at 50 ft, and if you do that on a 7/9, down you come).
The 700 and 900 have FADEC engines, and could have used push button start, as the Embraers using the same engines do, but to minimize differences requirements between FADEC and non-FADEC you start the engines with the thrust levers the same as the manually controlled engines of the 200.  It's mostly about trying to keep the cockpit environment, QRH procedures, and checklists and flows as similar as possible.
When Bombardier introduced the CRJ1000 however, the differences got to be too much for Transport Canada and dedicated sim time (one session) became a requirement for a 200/700/900 pilot to qualify on the 1000.  A lot of it was related to the length.  The sim session includes making a 180 turn during taxi to show that you know how much real estate it needs.  And when you land it, the fuselage being so long the nosewheel comes down quite a bit later than the mains (it's actually like two landings - you land the mains, then the nose in seemingly two separate actions, like a lot of heavies). Plus various system differences that made the gap between the 1000 and 200 a little more than TC could take.
It was a little strange because the break really should have been between 200 and 7/9/1000, because that's were the differences were most significant, both system and operating wise, but because the 1000 was the tail end charlie in the family, that's where TC made the cutoff, and it did have some impact on CRJ1000 sales (besides scope clause issues in the US)